1. Field of the Disclosure
The present disclosure relates to a process for the treatment of a lignocellulosic material with the addition of corn stillage to produce sugars and/or ethanol fermented therefrom. The process can incorporate an ammonia fiber explosion (AFEX) process to disrupt the lignocellulosic material. The biomass is treated with enzymes to produce the sugars.
2. Brief Description of Related Technology
In the United States, ethanol is primarily made from corn starch.1 There are two major industrial processes producing ethanol: wet milling and dry milling. In both processes, the extracted starch is cooked, liquified, saccharified by a mixture of enzymes (α-amylase and glucoamylase) and fermented to beer.2-5 The beer is passed through a distillation system to separate ethanol from water and other soluble solids, referred to as distiller's solubles (DS). During this process, a large amount of distiller's solubles is generated, also called “thin stillage.” In order to sell wet distillers grain (WDG) as useful byproducts, the stillage is concentrated and mixed with wet distillers grain, dried and marketed as distillers dried grains (DDG). Removal of water from corn-processing streams is costly in terms of energy (700-3000 kJ/kg of water, i.e., about 30% energy requirements of the entire plant) and involves the use of equipment that contributes to capital and operating expenses.1 
Ethanol processes face some difficult challenges if they are to improve competitiveness, profitability and sustainability while reducing co-product variability and energy costs. The nascence of the first generation corn stover lignocellulosic biorefinery will be through an existing dry or wet mill corn based ethanol industry. However, a commercially successful biorefinery will only come into existence through further reduction in processing costs.
Most of the current ethanol produced in the United States uses feed corn as a feedstock. Corn is the most important and economical source of starch in the United States. Starch is the major carbohydrate storage product in corn kernels comprising 70-72% of the kernel weight on a dry weight basis. Starch is readily converted to glucose using α-amylase and glucoamylase enzymes and fermented into ethanol using yeast. Today, most fuel ethanol is produced from corn by either the dry grind (67%) or the wet mill (33%) process. The key distinction between wet mill and dry grind facilities is the amount of water used in the process. Current technologies allow for 2.5 gallons (wet mill) to 2.8 gallons (dry grind) of ethanol per bushel of corn.
The wet milling process is more capital- and energy-intensive, as the grain must first be separated into its components, including starch, fiber, gluten, and germ. The germ is removed from the kernel and corn oil is extracted from the germ. The remaining germ meal is added to fiber and the hull to form corn gluten feed. Gluten is also separated to become corn gluten meal, a high-protein animal feed. The starch solution is separated from the solids and fermentable sugars are produced from the starch. These sugars are fermented to ethanol. The wet mill produces a number of high-value products. About 1.6 pounds of corn oil, 2.6 pounds of gluten meal, and 13.5 pounds of gluten feed are generated via this process per bushel of corn
In the dry grind process, the clean corn is ground and mixed with water to form a mash. The mash is cooked and enzymes are added to convert starch to sugar. Then yeast is added to ferment the sugars, producing a mixture containing ethanol and solids. This mixture is then distilled and dehydrated to create fuel-grade ethanol. The solids remaining after distillation are further dried to produce distillers' dried grains with protein and are sold as an animal feed supplement. For every bushel of corn, 17 pounds of DDGS are generated by this process.
In the dry grind process, the solid and liquid fractions remaining after distillation are referred to as “whole stillage.” Whole stillage includes the fiber, oil, and protein components of the grain, as well as the non-fermented starch. This co-product is a valuable feed ingredient for livestock, poultry, and fish. Although it is possible to feed whole stillage, it is usually dried further before being sold as feed to prevent microbial contamination. First, the “thin stillage” is separated from the insoluble solid fraction using centrifuges or presses/extruders. The stillage leaving the beer column is centrifuged with a decanter. Between 15% and 30% of the liquid fraction (thin stillage) is recycled as backset. The remainder is concentrated further by evaporation and mixed with the residual solids from the fermentation. After evaporation, the thick, viscous syrup is mixed back with the solids to create a feed product known as wet distiller's grains with soluble (WDGS). WDGS, containing 65% moisture, can be used directly as a feed product. In fact, it is often favored by dairy and beef feeders because cattle seem to prefer the moist texture. However, WDGS has a shelf-life of only 1-2 weeks. Unless the feedlot is within about 50 miles (80 km) of the ethanol plant, handling and storage can be a challenge, especially in hot summer months when shelf-life is very limited. To increase shelf-life and reduce transportation costs, WDGS is usually dried to about 10-12% moisture, to produce DDGS. Drying WDGS is energy-intensive, consuming about one-third of the energy requirements of the entire dry grind plant. However, producing a uniform, stable, high-quality feed co-product is essential to the profitability of the plant, resulting in most plants producing DDGS rather than WDGS. Currently, dry grind ethanol plants produce over 5.5×106 tons of DDGS per year, and the amount is increasing.
Objects
It is an object to minimize energy spent during conventional corn ethanol processes using corn stillage to reduce the processing cost and to optimize the utilization of water resources in combination with other processes. It is further an object to increase the glucan yield of from lignocellulosic material using the corn stillage, thereby also increasing the yield of a subsequent ethanol fermentation process.
These and other objects may become increasing apparent by reference to the following description and the drawings.